In the present years commercialization efforts for the synthesis of complex carbohydrates including secreted oligosaccharides have increased significantly due to their roles in numerous biological processes occurring in living organisms. Secreted oligosaccharides such as human milk oligosaccharides are becoming important commercial targets for nutrition and therapeutic industries. However, the syntheses and purification of these oligosaccharides and their intermediates remained a challenging task for science. One of the most important human milk oligosaccharides is 2′-O-fucosyllactose (2-FL, see Scheme 1) found in the highest concentration in mother's milk.

Several biological roles of 2′-O-fucosyllactose have been suggested including but not limited to its prebiotic, antibacterial, antiviral, immune system enhancing, brain development enhancing, etc. effects making it an attractive target for large scale production/isolation/purification for nutritional and therapeutic industries.
The first mention of 2′-O-fucosyllactose in the literature appeared in the 1950's by Kuhn et al. (Chem. Ber. 1955, 88, 1135; ibid. 1956, 89, 2513). According to the method by Kuhn syrupy or amorphous 2-FL isolated from mother's milk was dissolved in hot 75% methanol and abs. ethanol was gradually added in the presence of seed crystals. The seed crystals were produced in two ways: after “prolonged” storage some small crystals precipitated by the wall of the flask containing syrupy 2-FL, or 2-FL precipitated from a solution consisting of aqueous methanol, n-butanol and n-hexanol at 4° C. after “several” weeks. The crystalline 2-FL thus obtained had the melting point of 230-231° C. (decomposed), contained no constitutional water and was supposed to be the α-form.
At those times specific human milk oligosaccharides were isolated from human milk by using sophisticated chromatographic protocols (mainly paper chromatography). However, the purities of such early isolated samples are rather uncertain due to the high number of human milk oligosaccharide isomers present in mother's milk and due to lack of availability of high performance chromatography techniques which are nowadays usual in the investigation and resolution of such complex tasks. For example, 2′-O-fucosyllactose and 3-O-fucosyllactose are both present in human milk and their chromatographic separation have been solved decades later. Though 2-FL was reported as a crystalline compound by Kuhn in 1956, because of the considerations mentioned above the purity of the isolated sample is rather ambiguous. Furthermore, since that publication no other evidence, reference or indication on the crystalline existence or occurrence of 2-FL could have been found in the art, thus 2-FL is generally available and used as amorphous (lyophilized) solid.
Crystallization or recrystallization is one of the simplest and cheapest methods to separate a product from contaminations and obtain pure substance. In addition, providing one or more crystalline modifications (polymorphs) of a solid is an important factor in product development, because the different crystalline forms affect the compound's properties—for example thermodynamic stability, solubility, density, hygroscopicity, electrical properties (such as dielectric constant, conductivity), mechanical properties (such as friability, hardness, breaking strength, elasticity), optical properties (such as colour, transparency, refraction), etc. —diversely. It enlarges the repertoire of materials that a scientist has available for improving the product's characteristics. With respect of 2-FL there is still a need for crystalline product which may simplify isolation, purification and formulation problems so far envisaged.